1. Field of the Invention
The present invention relates to a multi display device and a method of controlling the same. More particularly, the present invention relates to a multi display device that includes a drive circuit and a backlight unit shared in common by multiple display panels, which may prevent degradation in display quality such as the occurrence of a ghost image due to a leakage current drawn from an activated display panel.
2. Description of the Related Art
A portable electronic device incorporating a display module may include a main display panel that displays a large amount of text and images and a sub display panel that displays a small amount of text and images. For example, in a mobile device such as a foldable mobile phone, the main display panel may be positioned in an inner surface of a cover of the foldable mobile phone to display the phone number of a caller upon an incoming call, a dynamic image, etc., whereas the sub display panel may be positioned in an outer surface of the cover to display time information, a battery level, etc.
Generally, a camera module incorporated within the mobile device is required to have high performance and display a moving picture. A thin film transistor (TFT) liquid crystal display panel having a relatively high response speed, high resolution and high color reproducibility may be used for the main display panel. On the other hand, a super twisted nematic (STN) liquid crystal display panel or a TFT liquid crystal display panel having a relatively low resolution and low color reproducibility may be used for the sub display panel.
The dual display device may meet the user's need for convenience and achieve a high level of performance. However, in the dual display device, the use of the two display panels may increase both cost and power consumption.
The dual display devices have various configurations with respect to a drive circuit. For example, separate drive circuits may be used to drive the respective display panels independently. In such a case, noise between the display panels may be reduced; however, the use of the separate driving circuits for respective display panels may increase the volume of an application device (e.g., mobile phone) and power consumption.
In another example, a common drive circuit may be used for two display panels to manage the respective resolutions of the two display panels, and the volume of the device may be reduced as a result. Moreover, the common drive circuit is relatively expensive, resulting in increased costs. In still another example, when the main display panel and the sub display panel need not be concurrently driven, a common drive circuit for the main display panel may be shared by the sub display panel, which generally has a relatively lower resolution than the main display panel.
When an image is to be displayed on the main display panel, only the main display panel is driven and the sub display panel is powered off. Similarly, when the image is to be displayed on the sub display panel, only the sub display panel is driven and the main display panel is powered off. Although the use of the common driver chip may result in lower device cost, noise and increased power consumption may occur due to an increase in parasitic capacitance of a wiring line.
To reduce noise and power consumption, the main display panel and the sub display panel may have separate row lines, while sharing common column lines. In the TFT display panel, an output of the row line is applied to a gate terminal of a cell transistor of a pixel so that the row line may also be referred to as a gate line. Similarly, because an output of the column line is applied to a source terminal of the cell transistor of the pixel, the column line may also be referred to as a source line.
FIG. 1 is a schematic view illustrating a dual display device with one driver chip. Referring to FIG. 1, the dual display device includes a sub display panel 110, a main display panel 130, a driver integrated chip (IC) 140, glass substrates 101 and 102 and a flexible printed circuit board (FPCB) 120. As shown in FIG. 1, instead of separate driver ICs for the respective display panels, one driver IC 140 is mounted on the glass substrate 102. The driver IC 140 may be mounted on the glass substrate 102 via a chip-on-glass (COG) technique or using amorphous silicon gate (ASG).
The main display panel 130 and the driver IC 140 are mounted on the glass substrate 102 and the sub display panel 110 is mounted on the glass substrate 101 that is connected with the glass substrate 102 through the FPCB 120. Therefore, to drive both the main display panel 130 and the sub display panel 110 using one driver chip, the main display panel 130 and the sub display panel 110 may share in common the column lines of the driver chip 140. Depending on whether an image is displayed on the main display panel 130 or sub display panel 110, a row drive signal and a column drive signal are controlled to display images on a corresponding display panel.
In the liquid crystal display panel, a backlight unit disposed at a rear of the liquid crystal display panel may be used to display images according to an adjusted light transmittance of liquid crystal. In a multi display device, multi display panels may share a common backlight unit to reduce the overall dimension of the display device and lower costs. For example, in a foldable mobile device employing two display panels, the main display panel may be disposed at an inner side of a folding part of the mobile device and the sub display panel may be disposed at an outer side of the folding part. The backlight unit may be disposed at the folding part and interposed between the main display panel and the sub display panel.
FIG. 2 is a schematic view illustrating a dual display device using a common backlight unit. In FIGS. 1 and 2, like reference numerals refer to similar or identical elements. As shown in FIG. 1, the glass substrate 101 is connected with the glass substrate 102 through the FPCB 120, wherein the main display panel 130 is mounted on the glass substrate 102 and the sub display panel 110 is mounted on the glass substrate 101. Referring to FIG. 2, the sub display panel 110 is rotated 180 degrees so that a rear face of the sub display panel 110 opposes a rear face of the main display panel 130. A backlight unit 150 is interposed between the main display panel 130 and the sub display panel 110. The backlight unit 150 may include a bi-directional light-emitting device so that the light may pass through both the main display panel 130 and the sub display panel 110.
When two display panels share a single driver chip and a single backlight unit, as described above, an output of the driver chip is commonly used for the main display panel and the sub display panel (i.e., column lines for the main display panel are shared by the sub display panel), and a minor amount of leakage current may flow through the sub display panel when a main display panel is activated. The leakage current through the sub display panel may be drawn through a capacitor in the pixel of the sub display panel to change the light transmittance of the pixel so that a ghost image may appear on the sub display panel. When the respective display panels each use a separate backlight unit, in order to display an image on the main display panel so that the ghost image may not appear on the sub display panel, only the backlight for the main display panel is turned on, while the backlight for the sub display panel is turned off.
However, when the backlight is shared in common by the main display panel and the sub display panel, light is transmitted to the sub display panel even when only the main display panel is activated. Therefore, the ghost image due to the leakage current may appear on the sub display panel so that the image will appear distorted to the viewer. Moreover, as described above, noise and increased power consumption may occur due to an increase in parasitic capacitance of a wiring line.